Spiral electrode with contact retainer

ABSTRACT

There is disclosed herein a bipolar fetal monitoring electrode having an electrode body, a spiral electrode terminating in a point for engaging with fetal scalp, and a reference electrode insulated from the spiral electrode. The end of the electrode from which the spiral extends includes one or more protrusions in the form of points, ramps, ribs or the like to increase the resistance of the spiral from unwinding from the fetal scalp to which it is attached and thus to help prevent the spiral from unwinding spontaneously.

BACKGROUND

The present invention relates to a bipolar electrode structureparticularly suitable for use in fetal heart monitoring.

Various forms of monitoring electrode structures have been developed.These include, for example, a body organ electrode shown in U.S. Pat.No. 3,416,534 which is arranged for insertion into the body through ahypodermic needle and to function as a pacemaker electrode, and asimilar type shown in U.S. Pat. No. 3,472,234. Both of these electrodeshave a spiral configuration for attachment to a body organ. Otherexamples are the implantable electrode shown in U.S. Pat. No. 3,737,579,and the double spiral fetal electrode shown in U.S. Pat. No. 3,750,650.

A type of electrode to which the present invention is particularlydirected is shown in greater detail in applicant's U.S. Pat. No.3,890,420 and U.S. Pat. No. 3,910,271, and in FIGS. 8-10 of Hon U.S.Pat. No. Re. 28,990. FIG. 1 of the present application illustrates thisform of prior art electrode which comprises a bipolar electrode formedby injection molding to form a body 12 having a first spiral electrode13 at the forward end thereof and a second wafer electrode 14 at therear end thereof. The first and second electrodes 13 and 14 are made ofa conductive metal such as stainless steel or the like, and each isrespectively connected to first and second insulated wire conductors 15and 16. The exposed surface of the wafer electrode 14 generally isapproximately twice the exposed surface area of the electrode 13. Theother ends of the conductors 15 and 16 are connected in a manner wellknown in the art to electronic monitoring equipment (not shown) suitablefor monitoring fetal heartbeat, heart rate or the like. U.S. Pat. No.3,890,420 discloses a method and molding apparatus for forming theelectrode structure of FIG. 1.

The spiral electrode of the type shown in FIG. 1 has been widelyaccepted and has overcome the various problems of the"forceps-endoscope" and the "sliding sleeve-clip" type of electrodes,both of which include clips but which must be squeezed onto the fetalepidermis. The spiral electrode of FIG. 1, on the other hand, can bereadily easily inserted through the vagina and cervix of a woman inlabor or about to be in labor by suitable applying devices of the natureshown in U.S. Pat. No. 3,910,271 and U.S. Pat. No. Re. 28,990 and, thus,in many instances can be quickly and effectively applied to the fetusduring an early stage of labor, and which can be quickly and easilyremoved.

However, it has been found through years of use of the form of spiralelectrode of the type shown in FIG. 1 that the doctor will apply oneelectrode by screwing into the fetal epidermis, but in many instances itcomes off and a second one (and sometimes even more) must be applied. Itgenerally is too cumbersome to attempt to reapply a first electrodewhich has become detached and, thus, that electrode usually is removedand another electrode applied. Because of the nature of the spiral, andthe "lead" or angle of the spiral -3, there is a tendency for the spiralto unwind or unscrew itself spontaneously or inadvertently from thefetal scalp after being connected to the fetal scalp by the doctor. Thisnot only necessitates one or more additional electrodes to be tried, butalso results in undue trauma to the fetal scalp.

The present invention involves a modification of a portion of the spiralelectrode of the type shown in FIG. 1 so as to provide improvedfrictional contact between a surface of the electrode and the fetal skinto thereby minimize the opportunity for the spiral to unwind itself.According to exemplary embodiments of the present invention, the surfaceof the spiral electrode which is to contact the fetal scalp is providedwith protrusions in the form of, for example, points, ribs, ramps or thelike to cause added friction or interference, or to gather scalp, so asto reduce or minimize the possibility for the spiral to unwind orunscrew spontaneously or inadvertently from the scalp.

Accordingly, it is a principal object of the present invention toprovide an improved form of spiral electrode.

Another object of this invention is to provide a spiral electrodewherein the end that contacts skin is modified to increase the frictionor interference between the electrode and the skin so as to minimizeloosening or unwinding of the electrode from the skin.

A further object of this invention is to provide a new form of fetalmonitoring spiral electrode having protrusions in the form of, forexample, a plurality of points, ramps, ribs or the like, molded in thesurface of the electrode which contacts the skin so as to minimizeinadvertent detachment of the electrode from the skin.

These and other objects and advantages of the present invention willbecome better understood through a consideration of the followingdescription, taken in conjunction with the drawings in which:

IN THE DRAWINGS

FIG. 1 is a perspective view of a conventional prior art fetalmonitoring spiral electrode;

FIG. 2a is a side elevational view and FIG. 2b is a partial top planview of a first embodiment of a modified spiral electrode according tothe present invention including protrusions in the form of points moldedas part of the electrode,

FIG. 3a is a side elevational view and FIG. 3b is a partial top planview illustrating another embodiment with protrusions in the form ofpoints molded as part of the electrode, and

FIG. 4a is a side elevational view and FIG. 4b is a partial plan view ofa third embodiment of an electrode having protrusions in the form ofthin ribs molded as part of the electrode.

Turning now to the drawings, and again to the prior art electrode inFIG. 1, the spiral 13 and wafer 14 electrodes are molded into theelectrode body 12 as previously discussed and as more fully describedin, for example, U.S. Pat. No. 3,890,420. The electrode of FIG. 1includes the cylindrical plastic body 12 which has a first, proximal end18 and a second, distal end 19. The spiral 13 of the electrode ispointed at 20 and when it is screwed into the fetal scalp, the first end18 of the body 12 normally, at least initially, is adjacent the skin,and the second end 19 is disposed away from the fetal scalp. Because ofthe "lead" or angle (like screw threads) of the spiral 13 as notedearlier, there is a tendency for the electrode to unwind or unscrewspontaneously from the fetal scalp.

Turning now to the exemplary embodiments shown in FIGS. 2-4, like partsbear like or similar reference numerals to those in FIG. 1. Thus, ineach of FIGS. 2 through 4 an injection molded electrode body isillustrated at 12a, and a spiral electrode 13, a wafer electrode 14, andone of the electrical conductors 15 are all shown (the spiral 13 ispartially omitted from FIGS. 2b, 3b and 4b for clarity). A differentreference numeral 12a is used for the plastic body of the electrodebecause a first, distal end 18a thereof is modified according to thepresent invention from the conventional electrode of FIG. 1. In eachinstance, the first surface 18a which confronts the skin of the fetus ismodified in a manner to increase the friction or resistance, or toprovide fetal skin gathering ability, so as to prevent or minimizespontaneous unwinding of the spiral 13 from the fetal skin.

In the arrangement shown in FIGS. 2a-2b, first and second protrusions inthe form of right angle points 22 and 24 are provided. These preferablyare molded into the body 12a during molding of the electrode. The points22 and 24 are basically right angle triangular in shape, with firstsurfaces 22a and 24a essentially parallel to the longitudinal axis ofthe electrode, and second surfaces 22b and 24b being inclined downwardlytoward the surface 18a from the respective apex 22c and 24c of thepoints. The heights of the points 22 and 24 typically may range fromapproximately 0.015 to 0.020 inch as illustrated in FIG. 2a, with 22being shorter than 24 so as to maintain about an equal distance betweenthe apexes 22c and 24c of these points and the spiral 13 (see FIG. 2a).Thus, the height difference of the points essentially is varied as theangle of the spiral 13. The points 22 and 24 may extend from the outerperiphery 26 (note FIG. 2b) radially inwardly partially toward thecenter of the surface 18a as best seen in FIG. 2b.

These points 22 and 24 molded as part of the electrode with one straightside (22a, 24a) serve to minimize the opportunity for the spiral tospontaneously unwind itself. However, the spiral can be readily easilyremoved from the fetal scalp by slightly pulling the electrode away fromthe scalp and unwinding the electrode. The points 22 and 24 thus act asan impediment to unscrewing the electrode from the fetal scalp byessentially digging into the flexible scalp or serving to gather theskin between points to thereby increase the friction between the surface18a and the scalp.

The embodiment shown in FIGS. 3a-3b is similar to that shown in FIGS.2a-2b, but in this case, protrusions in the form of points 32 and 34 areessentially in the form of forty-five degree triangles (when viewed fromthe periphery of the electrode as seen in FIG. 3a, thereby forminginclined sides (32a, 34a, and 32b, 34b) having an included angle offorty-five degrees extending to respective apexes 32c and 34c. As in theembodiment of FIG. 2, the points 32 and 34 can extend from the periphery26 of the electrode body 12a radially toward the center on the surface18a as best seen in FIG. 3b. The points 32 and 34 help to gather thescalp between these points so as to minimize the opportunity for thespiral to unwind spontaneously. A typical height for the ribs 32 and 34ranges from 0.010 to 0.015 inch as shown in FIG. 3a, with the rib 32being the shorter and rib 34 being the taller.

Turning now to the embodiment of FIGS. 4a-4b, the same illustrates apair of relatively thin ribs 42 and 44. In this embodiment, these ribsare rectangular as shown in FIG. 4 and extend radially from theperiphery 26 toward the center of the surface 18a. The tops 42c and 44ccan be flat as shown and substantially parallel to the surface 18a. Atypical thickness for these ribs is approximately 0.010 inch wide, withthe height of the two ribs 42 and 44 varying from approximately 0.010 to0.015 inch as shown in FIG. 4a. These thin ribs 42 and 44 causeinterference to help keep the spiral from unwinding spontaneously. Theseribs can be slightly flexible so as to bend and help to lock the scalpbetween the wire spiral 13 and the surface or base 18a.

The protrusions, such as the points and ribs as shown in FIGS. 2 through4, help to increase the friction or interference between the electrodebody 12a and the fetal skin either through their "roughness" to increasefriction or interference, or through gathering fetal skin between thepoints or ribs, and along with the slight resilience of the spiral 13 tothus help minimize unwinding of the spiral 13. On the other hand, theelectrodes still can be easily removed when necessary by pullingslightly on the conductors (e.g., 15 and 16) in a direction away fromthe fetal scalp (toward the bottom of the drawings in FIGS. 2a, 3a and4a) which helps pull the protrusions away from the skin because of theresilience of the spiral 13. Because of this action, including theslight flexibility of the spiral 13, the interference or resistance isreduced to thereby allow the spiral 13 to be unscrewed upon demand(e.g., after delivery) in a manner already well familiar to physicians.

While specific exemplary embodiments of configurations of points, ramps,ribs and the like have been shown and discussed, it will be apparent tothose skilled in the art that the shapes, numbers, widths, lengths, andthe like of these protrusions from the base or surface 18a of theelectrode can be modified in shape, number and the like, the importantaspect of the invention being that the base or surface 18a is modifiedor roughened in a manner to engage the fetal scalp and increase theresistance to spontaneous unwinding of the spiral from the scalp.

While embodiments of the present invention have been shown anddescribed, various modifications may be made without departing from thescope of the present invention, and all such modifications andequivalents are intended to be covered.

What is claimed is:
 1. An electrode structure for use in fetal heart monitoring comprisinga substantially cylindrical electrode body formed of electrically insulating material and having a first end and a second end, a spiral electrode extending from the first end of the body and terminating in a pointed end adapted to pierce a fetal epidermal layer, a second electrode extending from the second end of the electrode body, said second electrode being electrically insulated from the spiral electrode, and the first end of the electrode body having at least a protrusion underlying a portion of the spiral electrode to increase the resistance of the electrode structure from unwinding from the fetal epidermal layer.
 2. An electrode as in claim 1 with a plurality of said protrusions.
 3. An electrode as in claim 2 wherein said protrusions comprise a pair of points molded as part of the electrode body each having a straight side substantially parallel to a longitudinal axis of the electrode body.
 4. An electrode as in claim 2 wherein said protrusions comprise a plurality of points in the form of substantially forty-five degree triangles extending from the first end and terminating in apexes underlying a part of the spiral electrode.
 5. An electrode as in claim 2 wherein said protrusions comprise a plurality of relatively thin ribs extending from said first surface.
 6. An electrode as in claim 2 wherein each of said protrusions extends to a height from the first end of the electrode body different than that of any other protrusion in the plurality of protrusions.
 7. An electrode as in claim 6 wherein said protrusions extend from the first end to form apexes underlying portions of the spiral electrode, and the apexes are substantially equidistant from the portions of the spiral electrode which they underlie.
 8. An electrode structure for use in fetal heart monitoring comprisingan elongated and substantially cylindrical electrode body formed of electrically insulating material and having a first end and a second end, a spiral electrode extending from the first end of the body and terminating in a pointed end adapted to pierce a fetal epidermal layer, a second wafer electrode extending from the second end of the electrode body, said second electrode being electrically insulated from the spiral electrode, electrical conductors connected to the respective spiral and wafer electrodes, and the first end of the electrode body having a plurality of protrusions underlying a portion of the spiral electrode and arranged substantially equidistant from a portion of the spiral electrode to increase the resistance of the electrode structure from unwinding from the fetal epidermal layer.
 9. An electrode as in claim 8 wherein said protrusions comprise a pair of points molded as part of the electrode body each having a straight side substantially parallel to a longitudinal axis of the electrode body and an inclined side.
 10. An electrode as in claim 9 wherein said protrusions extend from the first end to form apexes underlying portions of the spiral electrode.
 11. An electrode as in claim 8 wherein said protrusions comprise a plurality of points in the form of substantially forty-five degree triangles extending from the first end and terminating in apexes underlying a part of the spiral electrode.
 12. The electrode of claim 11 wherein the protrusions contact each other.
 13. An electrode as in claim 8 wherein said protrusions comprise a plurality of relatively thin ribs extending from said first end.
 14. The electrode of claim 13 wherein the protrusions are slightly flexible.
 15. The electrode of claim 8 wherein the protrusions are straight and not parallel to each other.
 16. The electrode of claim 8 wherein the protrusions are grouped sufficiently close together to permit gathering of the fetal epidermal layer between them.
 17. An electrode comprisinga substantially cylindrical electrode body having a first end and a second end, a spiral electrode extending from the first end and having a pointed end, a second electrode extending from the second end of the electrode body, said second electrode electrically insulated from the spiral electrode, electrical conductors connected to the spiral and second electrodes, a first protrusion on the first end of the electrode body extending radially inwardly from a peripheral cylindrical edge of the electrode body and at least partly underlying the spiral electrode, and a second protrusion on the first end of the electrode body extending radially inwardly from the peripheral cylindrical edge of the electrode body and at least partly underlying the spiral electrode, the first protrusion having a first height and the second protrusion having a second height, greater than the first height, over the first end of the electrode body, such that the first protrusion and the second protrusion are substantially equally spaced apart from the spiral electrode.
 18. The electrode of claim 17 wherein the first protrusion is adjacent the second protrusion.
 19. An electrode structure for use in fetal heart monitoring comprisinga substantially cylindrical electrode body formed of electrically insulating material and having a first end and a second end, a spiral electrode extending from the first end of the body and terminating in a pointed end adapted to pierce a fetal epidermal layer, a second electrode extending from the electrode body, said second electrode being spaced from and electrically insulated from the spiral electrode, and the first end of the electrode body having at least a protrusion underlying a portion of the spiral electrode to increase the resistance of the electrode structure from unwinding from the fetal epidermal layer. 